This invention relates to screen panels, and in particular to screen panels used in vibratory screening operations.
In a vibratory screening operation, material which is to be screened is deposited on a vibrating screen deck. It is now common practice for the screen decks to have a frame and for the actual screening surface of the deck to be provided by a large number of individual screen panels which are mounted on the frame in side-by-side relationship with one another.
One particularly successful design of screen panel is that supplied by the applicant under the designation VR-X panel. This panel, which is described in ZA 2002/5151, has a rectangular outer frame defined by parallel side members and parallel end members at right angles to the side members. The screening surface of the panel is provided by arrays of parallel, flexible, elongate screen elements which are oriented generally diagonally with respect to the outer frame and span internally between members of the frame. Each of these elements has a regular zigzag profile, when viewed in plan, such profile being defined by alternating first and second portions of the elements which are generally parallel to the side members of the outer frame and generally parallel to the end members of the outer frame respectively.
The profiles of adjacent elements are out of phase with one another such that the elements define generally rectangular screen apertures between them and furthermore such that the zags of adjacent elements, where the first and second portions meet one another in each profile, are close to one another.
The overall screen surface of the screen deck is made up of the individual screen surfaces of the screen panels described above. During a screening operation, the screen deck is vibrated and particulate material is deposited on it. The configuration and vibration is such that the material migrates in a preferential feed direction on the screen deck, with the screen apertures allowing undersize particles of the material to pass through the screen surface while oversize material continues its migration in the feed direction, thereby achieving sizing of the material into undersize and oversize fractions.
While the known VR-X panels have been found to perform well in many applications, there are some instances where the flexibility and shape of the screen elements, and their geometrical relationship to one another, allow them to flex excessively apart from one another, effectively expanding the screen apertures to a size which allows particles that are unacceptably large, i.e. oversize particles, to pass through. An example is where particles derived from iron ore mining operations are screened, and the particles tend to have an elongate shape, for example a tapering, carrot-like shape.
It can happen that the pointed end of an oversize particle may lodge in a screen aperture but still be forced through the aperture as overlying material presses down on the particle and causes the aperture to expand by flexing the screen elements apart from one another.
The end result in such situations can be inaccurate screening of the ore material.
A further disadvantage of the known VR-X design is that some of the screen apertures are less than full size, leading to an overall reduction in the overall screening area and, as a result, a reduction in screening efficiency.